Gridded bathymetry (5m) of the shelf environment of Nihoa Island, Hawaii, USA.
This netCDF grid includes multibeam bathymetry from the Simrad EM120, Simrad EM1002,
Simrad EM300, and Simrad EM3002d multibeam sonars collected as of December 2006 by
the NOAA Coral Reef Ecosystem Division in depths between 20 and 500 meters.

Purpose:

The netCDF grid was created using data gathered from multibeam soundings for use
as a planning and reference document. The data are also being used for benthic habitat mapping,
for locating Essential Fish Habitat, and for studying geologic features of the area.
Refer to supplemental information for description of instrument and survey.

Supplemental_Information:

Multibeam data were collected aboard the NOAA Ship Hi'ialakai, a 218' United States
National Oceanographic and Atmospheric Administration research ship. The NOAA
Ship Hiialakai's survey sensors include a 30 kHz Simrad EM300 sonar
and a 300 kHz Simrad EM3002d sonar, which provide bathymetry and
imagery data, a TSS/Applanix POS/MV Model 320, which measures position,
velocity, attitude and heading, and a Seabird SBE 9/11 plus CTD used to
measure sound velocity profiles.

These data are not to be used for navigation purposes.
Please acknowledge NOAA and the Joint Institute for Marine and Atmospheric
Research (JIMAR) University of Hawaii as the sources of this information.

netCDF file created using the Generic Mapping Tools
(GMT) in a LINUX environment

Data_Quality_Information:

Attribute_Accuracy:

Attribute_Accuracy_Report:

Data are collected for resource management
and research purposes and are tested for internal consistency; however,
no effort is made to compare these data to external references or to
other published data.

Logical_Consistency_Report:

These data are believed to be logically consistent
though no tests were performed

Multibeam swath files are acquired in the Generic Sensor Format (GSF) and
are edited on a swath by swath basis using SAIC's SABER editing software.
The edited swath files are then combined into a Pure File Magic (PFM) format
in SABER and area based editing is performed. The edited PFM is then exported
as X,Y,Z points with a defined grid cell size and the points are combined
with X,Y,Z IKONOS estimated depth points. The resulting X,Y,Z data are then
gridded using xyz2grd, a Generic Mapping Tools (GMT) algorithm that converts
an ASCII or binary table to a netCDF grid file format. GMT is an open source
collection of tools for manipulating geographic data sets. Grid nodes with more
than one value are set to the average value and unconstrained nodes are set to
NaN. Finally, the netCDF grid is clipped at a depth that minimizes data gaps
for the specified grid cell size and then converted to an ArcGIS ASCII file
format using LINUX/UNIX commands in combination with GMT. Additional information
about GMT can be found at: www.soest.hawaii.edu/gmt and additional information
about the multibeam data processing is recorded in the cruise metadata.

Process_Date: 20061201

Spatial_Data_Organization_Information:

Direct_Spatial_Reference_Method: Raster

Raster_Object_Information:

Raster_Object_Type: Grid Cell

Row_Count: 7810

Column_Count: 14344

Vertical_Count: 1

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:

Planar:

Grid_Coordinate_System:

Grid_Coordinate_System_Name: Universal Transverse Mercator

Universal_Transverse_Mercator:

UTM_Zone_Number: 4

Transverse_Mercator:

Scale_Factor_at_Central_Meridian: 0.9996

Longitude_of_Central_Meridian: -159

Latitude_of_Projection_Origin: 0

False_Easting: 500000

False_Northing: 0

Planar_Coordinate_Information:

Planar_Coordinate_Encoding_Method: Row and Column

Coordinate_Representation:

Abscissa_Resolution: 5

Ordinate_Resolution: 5

Planar_Distance_Units: meters

Geodetic_Model:

Horizontal_Datum_Name: D_WGS_1984

Ellipsoid_Name: WGS_1984

Semi-major_Axis: 6378137.000000

Denominator_of_Flattening_Ratio: 298.257224

Vertical_Coordinate_System_Definition:

Depth_System_Definition:

Depth_Datum_Name: mean lower low water

Depth_Resolution: 0.01

Depth_Distance_Units: meters

Depth_Encoding_Method: Attribute Values

Entity_and_Attribute_Information:

Overview_Description:

Entity_and_Attribute_Overview:

Depth values are real values based on the average of the
soundings that fell within the extracted grid cells. The number of
soundings per grid cell range from >1000 soundings in shallow depths
to as few as 20 soundings in deeper areas. A total error budget for
this survey has not been developed. Therefore, the accuracy of depth
measurements should be considered to be within 1 meter.

These data are not to be used for navigational purposes.
NOAA makes no warranty regarding these data, expressed or implied, nor
does the fact of distribution constitute such a warranty. NOAA cannot
assume liability for any damages caused by any errors or omissions in
these data, nor as a result of the failure of these data to function
on a particular system.